Preparation of non solvated aluminum hydride

ABSTRACT

1. A process for the preparation of non-solvated aluminum hydride which comprises (A) reacting hydrogen chloride with an excess of an alkali metal aluminum hydride of the formula:

United States Patent [1 1 Kraus et al.

[451 Sept, ii, 1973 PREPARATXON OF NON-SOLVATED ALUMINUM HYDRIDE [75] Inventors: Theodore C. Kraus, Cheshire;

Donald J. Mangold, Orange, both of Conn.

[73] Assignee: Olin Mathieson Chemical Corporation, New Haven, Conn.

221 Filed: Oct. 23, 1965 21 Appl. No.: 505,314

[52] U.S. Cl 423/645, 149/19, 149/60,

149/76, 149/77 [51] Int. Cl C0lb 6/00 [58] Field of Search 23/204; 423/645 [56] References Cited OTHER PUBLICATIONS Rice, Jr. PB. Report 127, 867, Non-Solvated Aluminum Hydride, 1956, pages 2 and 3 OD 181 A4 T9. Cotton, Progress In inorganic Chemistry, Vol. Ill, 1962, page 491 OD 151 P7.

Primary ExaminerLeland A. Sebastian Attorney-Walter D. Hunter, Donald F. Clements, Richard S. Strickler and George J. Koeser EXEMPLARY CLAIM 1. A process for the preparation of non-solvated aluminum hydride which comprises; (A) reacting hydrogen chloride with an excess of an alkali metal aluminum hydride of the formula:

M All-l where M is an alkali metal selected from the group consisting of lithium, sodium and potassium and in the presence of a lower dialkyl ether of the formula:

R OR

wherein R and R are alkyl radicals having 1 to 5 carbon atoms, the mole ratio of the said hydrogen chloride reacted with the said alkali metal aluminum hydride being within the range of from about 0.33 to about 0.95; (B) separating liquid and solid phases of the resulting reaction mixture and adding from about 0.05 to 0.20 mole of lithium borohydride per mole of starting alkali metal aluminum hydride to the said liquid phase; (C) adding an aromatic hydrocarbon selected from the group consisting of benzene, toluene and xylene in an amount of from 1 to about 6 times by volume of the said liquid phase; (D) removing the major portion of the lower dialkyl ether to yield a slurry containing solvated aluminum hydride; (E) heating the said slurry at a temperature of from about 35 to about 100 C. and for a period of time sufficient to remove the lower dialkyl ether associated with the aluminum hydride whereby a non-solvated aluminum hydride product is obtained and (F) recovering the non-solvated aluminum hydride.

4 Claims, No Drawings PREPARATION OF NON-SOLVATED ALUMINUM HYDRIDE This invention relates to the preparation of macrocrystalline, non-solvated aluminum hydride. More particularly, this invention relates to a process in which hydrogen chloride is reacted with an excess of lithium aluminum hydride in the presence of a solvent following which the non-solvated aluminum hydride is finally recovered from mixed solvent system.

Aluminum hydride is useful as a reducing agent, as a fuel in solid propellants, and as an intermediate. The non-solvated aluminum hydride of this invention when incorporated with oxidizers is capable of being formed into a wide variety of grains, tablets, and shapes, all with desirable mechanical and chemical properties. Propellants produced by the methods described in this application burn uniformly without disintegration when ignited by conventional means, such as a pyrotechnic type igniter, and are mechanically strong enough to withstand ordinary handling.

Although a great number of attempts have been made to prepare non-solvated aluminum hydride, the end result has been the formation of either an impure polymeric product or a solid solvated polymer from which the removal of all of the solvent without decomposition could not be achieved. Finholt .et al, (JACS, 69, 1199-1203 (1947)) reacted lithium aluminum hydride with aluminum chloride in the presence of diethyl ether and obtained a solid with a variable composition. Although the ratio of hydrogen to aluminum in the solid was 3:1 within experimental error, the total weight of the aluminum and the hydrogen in the solid product was always less than the total weight of the sample, the difference being the weight of the diethyl ether in the solvated compound. Hurd (Chemistry of the Hydrides, 1952, John Wiley and Sons, lnc., pages 95-98) presents a thorough review of laboratory methods for the preparation of solvated-aluminum hydride. Hurd states that aluminum hydride never has been isolated except in the form of a highly polymerized compound having the general formula (Alli- Further, Hurd states the lithium aluminum hydride can be reacted with aluminum chloride in ether solution to form lithium chloride and a solution of aluminum hydride in ether and that this solution of aluminum hydride cannot be evaporated to obtain a volatile aluminum hydride. Chizinsky et al, (JACS, 77, 3164-5, (1955)) have described a method for the preparation of nonsolvated aluminum hydride. First, a solution of aluminum hydride in diethyl ether was prepared by reaction of lithium aluminum hydride and aluminum chloride. The solution of aluminum hydride was filtered promptly (before polymerization could occur) through sintered glass under nitrogen into an inert liquid (pen' tane or ligroin were found to be suitable). Chizinsky et al state it is essential that the hydride solution be rapidly mixed with a relatively large volume of the inert liquid and that a satisfactory method is to run the solution in a thin film down a wire while the precipitant is vigorously stirred by a magnetic stirrer. On drying the reresulting fluffy precipitate under vacuum at room temperature for at least twelve hours, a product was obtained which on analysis was shown to correspond to aluminum hydride.

1n the process of this invention, hydrogen chloride is reacted with an excess of an alkali metal aluminum hydride dissolved in a lower dialkyl ether to yield aluminum hydride, the alkali metal chloride and hydrogen. The reaction takes place according to the following equation:

MAll l, HCl AlH MCl H wherein M is an alkali metal selected from the group consisting of lithium, sodium and potassium. The alkali metal chloride, being insoluble in the lower dialkyl ether, precipitates during the reaction and is removed by a convenient method, such as by filtration. Hydrogen generated during the reaction is allowed to escape from the reactor and is measured to determine the extent of the reaction. After removal of the insoluble alkali metal chloride by filtration or by any other convenient method, a quantity of an ethereal solution of lithium borohydride can be added, if desired, to the clear liquor. Lithium borohydride aids in desolvation and improves particle crystallinity. Other additives which improve the thermal stability of the final non-solvated aluminum hydride, such as mercury can also be added at this point in the process. Generally from about 0.05 to 0.20 mole of lithium borohydride per mole of starting alkali metal aluminum hydride is employed.

The temperature of the reaction will generally be from about 25 C. to about 50 C. with the preferred temperature being from about -10 C. to about 32 c.

In carrying out the reaction any of the lower dialkyl ethers can be employed. Suitable lower dialkyl ethers include ethyl ether, n-propyl ether, n-butyl ether, namyl ether, methyl ethyl ether, methyl propyl ether, methyl butyl ether, ethyl propyl ether, ethyl butyl ether, propyl butyl ether, isopropyl ether, isobutyl ether, isoamyl ether, methyl isopropyl ether, methyl isobutyl ether, ethyl isobutyl ether, ethyl isopropyl ether, ethyl isobutyl ether, ethyl isoamyl ether, etc.

In conducting the reaction it is advantageous to maintain the intial concentration of the alkali metal aluminum hyride at about 1 to about 7.0 per cent by weight based on the weight of the lower dialkyl ether employed. The proportion of ether to the reactants not only affects the solubility of the reactants but also the extent of solution of the aluminum hydride in the reaction mixture and control of the reaction temperature. In the applicants novel process it has been found that an excess of the alkali metal aluminum hydride must be employed. Although the role of the excess of the alkali metal aluminum hydride is not fully understood, it is known that the excess of the alkali metal aluminum hydride participates in the solubilization of the aluminum hydride formed in the reaction and, in addition, it appears to play a significant role in the applicants process in that it makes possible a facile and complete desolvation of the aluminum hydride. The molar ratio of the hydrogen chloride to the alkali metal aluminum hydride employed can be varied widely from about 0.33 to about 0.95 with the preferred molar ratio being from about 0.74 to about 0.95.

In the next step in the process, to the ethercontaining solution of aluminum hydride there is added a quantity of aromatic hydrocarbon solvent selected from the group consisting of benzene, toluene and xylene. Usually the volume of the aromatic material employed will be from about 1 to 6 times the volume of the ethereal solution. In the next step the mixture of the aromatic hydrocarbon solvent and the lower dialkyl ether containing the aluminum hydride product is disdialkyl ether tilled to remove the major portion of the ether, so that the resulting solution contains between about 2 and about 10 weight per cent ether. During this distillation step crystalline solvated aluminum hydride precipitates out. The pressure during the distillation operation can be varied widely and generally will be maintained from about atmospheric to about 100 mm. Hg. In the next step, the ether is removed from the solvated product by increasing the temperature. It is recommended that during the desolvation step the mixture be stirred at a rate of from about 6 r.p.m. to about 120 r.p.m. or more and the slurry containing the solvated aluminum hydride be heated rapidly to 95 C. and maintained between 95 and 100 C. for a period of 0.3 to 1 hour or more at ambient pressure. In the final step, the product is recovered by filtering the slurry or by any other convenient method; washing with a lower dialkyl ether, such as diethyl ether, and then drying the white, nonsolvated, aluminum hydride in crystalline form under vacuum conditions or by moderate heating at atmospheric pressure. Other recovery schemes can be employed, if desired.

The non-solvated aluminum hydride produced by practicing the method of this invention can be employed as an ingredient of solid propellant compositions in accordance with general procedures which are well understood in the art, inasmuch as the nonsolvated aluminum hydride produced by practicing the present process is readily oxidized using conventional solid oxidizers, such as ammonium perchlorate, potassium perchlorate, sodium perchlorate, ammonium nitrate and the like. In formulating a solid propellant composition employing non-solvated aluminum hydride and from 65 to 90 parts by weight of oxidizer, such as ammonium perchlorate, are present in the final propellant composition. In the propellant, the oxidizer and the product of the present process are formulated in intimate admixture with each other, as by finely subdividing each of the materials separately and thereafter intimatly admixing them. The purpose in doing this, as the art is aware, is to provide proper burning characteristics in the final propellant. In addition to the oxidizer and the oxidizable material, the final propellant can also contain an artificial resin, generally of the ureaformaldehyde or phenol-formaldehyde type, the function of the resin being to give the propellant mechanical strength and at the same time improve its burning characteristics. Thus, in manufacturing a suitable propellant, proper proportions of finely divided oxidizer and finely divided non-solvated aluminum hydride can be admixed with a high solids content solution of a partially condensed urea-formaldehyde or phenol formaldehyde resin, the proportions being such that the amount of the resin is about to 10 per cent by weight, based upon the weight of the oxidizer and the nonsolvated aluminum hydride. The ingredients are thoroughly mixed with simultaneous removal of the solvent, and following this the solvent-free mixture is molded into the desired shape, as by extrusion. Thereafter, the resin can be cured by resorting to heating at moderate temperatures. For further information concerning the formulation of solid propellant compositions, reference is made to US. Pat. No. 2,622,277 to Bonnell et al, and US. Patent No. 2,646,596 to Thomas et al.

The following examples will serve to further illustrate this invention:

EXAMPLE I The apparatus employed consisted of a three-necked flask equipped with a gas inlet tube reaching below the surface of the liquid, thermometer, reflux condenser, mercury-sealed stirrer, and a wet-test meter which was connected to an outlet from the flask.

Over a period of 30 minutes 50 g. (1.24 moles) of lithium aluminum hydride (95 per cent) was dissolved with stirring in 2 liters of diethyl ether. This solution was then cooled to 0 with an ice-water bath, and the hydrogen chloride addition begun. The extent of reaction was monitored by measuring the hydrogen evolution, and the final reading was confirmed by weighing of the hydrogen chloride cylinder before and after reaction. While the reaction mixture was maintained at 5l0 C., the hydrogen chloride was added over a 55- minute period, liberating 26.08 liters of hydrogen at 23 C. and 760 mm. of Hg. pressure (at S.T.P. 23.711 1.; 1.06 moles).

The reaction mixture was then allowed to stand for 30 minutes, permitting the lithium chloride to settle, and 1600 ml. of supernatant solution was filtered into a 12 liter, three-necked flask containing 174 ml. of 0.9 M. ethereal lithium borohydride solution. To this was added 6400 ml. of toluene. The solution was then filtered to eliminate the slight residue which developed and was then distilled under the following conditions:

. pres- Vol. Bath Pot. Head sure dismp. temp. temp. (mm. tilled Time (min) C) 0) C.) Hg.) (1111.)

1 Solution very slightly cloudy, stirring slowed to 8 r.p.m. 2 Discrete particles evident. a Cooling bath applied.

During this heating pattern, the pot was connected through a distillation head and water-cooled condenser to a receiver maintained at 78 C. After bringing the pot to atmospheric pressure with nitrogen, the cooled receiver effected a slight vacuum on the system (closed via mercryy bubble-off) throughout the subsequent heating period, and very slow distillation was evident. Following the heating period, the slurry was filtered and the collected solids washed by slurrying with 400 ml. of dried ether. A small amount of grayish material remained in suspension and was removed by decantation (2.5 g.). The remaining white product was washed several times with ether and dried under vacuum for 2 hours to yield 19.1 g. of non-solvated aluminum hydride (75 per cent of the theoretical amount).

5 I Al H C Cl% Li After cooling, the precipitate was isolated by filtra- Anal ggf fli 232% $8 04 0 23 O 3 tion and then stirred for about l/2 hour in about 150 39:74 10:2 0: ml. of ether (distilled from lithium aluminum hydride).

The ether was removed by decantation after which the 5 white, crystalline particles of product were then EXAMPLE H washed on the filter with three SO-ml. portions of ether in a dry nitrogen atmosphere, approximately 620 ml. and f y Placed under Vacuum (about 1 g) to of the aluminum hydride ether solution (0.328 moles y for two hours- Approximately g P All-l containing 17.6 mole per cent excess (0.070 yield) of the theoretical quantity of crystalline, white moles) of lithium aluminum hydride (prepared as de- 10 non-solvated aluminum was Obtainedscribed in Example I by reacting in diethyl ether hydrogen chloride with an excess of lithium aluminum hy- Percent dride and then removing the lithium chloride formed A1 H 0 Li Hg B 01 by filtration) was placed in a 5-liter flask containing 68 1 10,08 ml. ofa 1 M solution of Lint-1,, 0.056 mole) in ether. Found gggg 104 (l3 M1 3 This mixture was then diluted with 3500 ml. of toluene. The resulting cloudy mixture containing (16.5 per cent diethyl ether and 83.5 per cent toluene) was pressure EXAMPLES In To filtered through a medium porosity sintered glass disc S l dditi l im nts wer conducted in C vered with g a WOOl into a five liter, three-necked the same manner as described in Examples 1 and II. The flask which had been baked dry and cooled in a nitrol i h d id olution in ether was prepared by g m phere App m y 1 mole) of reacting an excess of lithium aluminum hydride with mercury was then added. 77 hydrogen chloride in diethyl ether and then removing The five-liter flask was then equipped with a therthe lithium chloride formed by filtration. Pertinent demometer, magnetically driven paddle stirrer and a distails are included in Table i which follows:

TABLE 1 w Aluminum hydride ether solution Ratio Excess hydro- Distillation Conversion Elemental Yield LiAlHl Hydrocarbon analysis Vol. (mole carbon to ether Temp. Time Temp. Time Per- Product Experiment N0. (1111.) percent) added (byvoL) 0.) (hr.) 0.) (min.) Al H C Grams cent formed 625 17 Toluene... 6.2 45 4.3 97-98 40 9.4 0.5 8.3 87 Granular. 600 17 6.2 45 5. 75 95-97 45 .4 0.6 7.2 76 Do. 620 17 -d0. 6.2 45 2.25 95-98 .1 0.3 6.2 600 17 6.2 42-46 2.5 97-99 45 .9 1.9 600 17 6.2 -43 4.0 97-99 .5 1.6 300 17 6.2 41-51 2.2 95-100 .5 1.0 600 17 6.2 43-50 3.0 95-100 45 .6 0.9 600 17 6.2 40-50 2.6 95-100 35 .5 0.5 300 17 Benzene 6.2 45 1.5 30 45 .5 3.1 250 17 do 0.2 42 1.8 60 .9 1.8 Needles.

I Lithium borohydrido added to solution. b Mercury added to solution.

tillation head, with thermometer, a water-cooled con- EXAMPLE x111 denser and receiver. The receiver was connected to a MW source of dry nitrogen and vacuum. The apparatus was 45 50 grams of lithium aluminum hydride of per cent laced in a three-liter three-necked roundsealed from the atmosphere by a mercury bubble-off. pumy was p The five-liter flask was then placed in an oil bath prebottomed fl which had been purged wlth dry mtro' heated to 5 the stirrer was Set at about 60 rpm gen. Two liters of diethyl ether was then added and the and the receiver was cooled with dry Distillation mixture stirred until the lithium aluminum hydride was 50 a was then conducted under the following conditions: dlssolved' The hydrogell chlonde was added at a rate of 0.53 mole per mm.. Hydrogen off-gas was measured with a wet-test meter and when it was determined Pros- Tnmmmtums Q by gas measurement that 1.06 moles of lithium alumi- (111m. 'lllnu llnth l'ot linml ll z.) Rmnnrks 55 num hydnde had reacted the addltlon hydfogen Y j u" m k h Mi b m H e chloride was stopped. 1600 ml. of the reaction mixture L, 1 R 1 5 i, -j 4;; H ,i'ij l dfyfi iil g ,3 12%; was then filtered into a 5-llter flask following which L" ll 22 S OW y. (ii i IODW 50 S I lit) M 45.0 30 tllhitlon maintained by 3200 P toluene and of a molar l' n 4a n; hdlu stpig plf'ossurol Wh to borohydrlde ether solution was added. Tl'llS solution iihjjj; 55 ii ill iili vlllllihliilliahilii fiilihohsmmi. was then filtered in a five-liter. three-necked, round- (115mm 60 bottomed flask, which was fitted with magnetic stirrer.

This water-white solution was heated as shown below:

The mixture, after standing overnight, was heated in Pres V01 the oil bath from room temperature (18 C.) to 95 C. Bath Pot sure dis in 85 minutes and then maintained at 95 97 C. for 65 i2 3? temp' C-) Hg.) (rnl.) Remarks 35 minutes. A slight vacuum was applied after reaching 55 34 266 0 Solution water white. 95 C. to affect a slow distlllatlon (670 to 650 mm. Hg 68 47 305 500 pressure). After 35 minutes the flask was removed 61 50 251 slghtly cmudy' 61 50 230 1,000 Granules formed.

from the bath. 51 .6 0

The resulting slurry was filtered and the product washed with dry diethyl ether. The non-solvated aluminum hydride product which was dried under vacuum, was obtained in 60 per cent yield.

Percent Anal. calc'd for AlH; 89. 92 10.08 Found 9.8 0. 4 0. 13

What is claimed is: l. A process for the preparation of non-solvated alu-' minum hydride which comprises (A) reacting hydrogen chloride with an excess of an alkali metal aluminum hydride of the formula:

M AIH v a where M is an alkali metal selected from the group consisting of lithium, sodium and potassium and in the presence of a lower dia lkyl ether of the formula:

wherein R and R are alkyl radicals having 1 to 5 carbon atoms, the mole ratio of the said hydrogen chloride reacted with the said alkali metal aluminum hydride being within the range of from about 0.33 to about 0.95; (B) separating liquid and solid phases of the resulting reaction mixture and adding from about 0.05 to 0.20 mole of lithium borohydride per mole of starting alkali metal aluminum hydride to the said liquid phase; (C) adding an aromatic hydrocarbon selected from the group consisting of benzene, toluene and xylene in an amount of from 1 to about 6 times by volume of the said liquid phase; (D) removing the major portion of the lower dialkyl ether to yield a slurry containing solvated aluminum hydride; (E) heating the said slurry at a temperature of from about 35 to about 100 C. and for a period of time sufficient to remove the lower dialkyl ether associated with the aluminum hydride whereby a non-solvated aluminum hydride product is obtained and (F) recovering the non-solvated aluminum hydride.

2. The process of claim 1 wherein the reaction is carried out at a temperature within the range of from about 25 C. to about 50 C.

3. The process of claim 1 wherein the said alkali metal aluminum hydride is lithium aluminum hydride.

4. The process of claim 1 wherein the said lower dialkyl ether is diethyl ether. 

1. A PROCESS FOR THE PREPARATION OF NON-SOLVATED ALUMINUM HYDRIDE WHICH COMPRISES (A) REACTING HYDROGEN CHLORIDE WITH AN EXCESS OF AN ALKALI METAL ALUMINUM HYDRIDE OF THE FORMULA:
 2. The process of claim 1 wherein the reaction is carried out at a temperature within the range of from about -25* C. to about + 50* C.
 3. The process of claim 1 wherein the said alkali metal aluminum hydride is lithium aluminum hydride.
 4. The process of claim 1 wherein the said lower dialkyl ether is diethyl ether. 